Estrogens are the primary female hormones responsible for the development and regulation of the female reproductive system and secondary female sex characteristics. Estrogens also have pleotropic roles in protein synthesis, coagulation, lipid balance, fluid balance, melanin, gastrointestinal track function, lung function, cognition, immune response and heart disease, among others.
The estrogen receptor (“ER”) is a ligand-activated transcriptional regulatory protein that mediates induction of the variety of biological effects through its interaction with endogenous estrogens, including 17β-estradiol and estrones. ER has been found to have two isoforms, ER-α and ER-β, and both receptors are involved in the regulation and development of the female reproductive tract.
ERs and estrogens regulate biological processes through several distinct pathways. The classical pathway involves the binding of a ligand-activated ER to a specific DNA sequence motif called an estrogen response element (ERE). ERs can also participate in non-classical pathways such as ERE-independent gene transcription via protein-protein interactions with other transcription factors, non-genomic pathways with rapid effects, and ligand-independent pathways that involve activation through other signaling pathways. This ER signaling is not only crucial for the development and maintenance of female reproductive organs, but also for bone metabolism and mass, lipid metabolism, cardiovascular protection, and central nervous system signaling.
Research in this area has confirmed the enormous complexity of estrogen and ER activities. A goal of drug development has been to create new compounds that modulate estrogen activity, either by acting as an antagonist or an agonist, or a partial antagonist or partial agonist.
One goal has been to identify complete anti-estrogens (complete antagonists) that have the effect of shutting down all estrogenic activity in the body. Fulvestrant is an example of a complete estrogen receptor antagonist with no agonist activity. It is a selective estrogen receptor downregulator (SERD). Fulvestrant was disclosed by Imperial Chemical Industries (ICI) in U.S. Pat. No. 4,659,516 and is sold by AstraZeneca under the name Faslodex. It is indicated for the treatment of hormone receptor positive metastatic breast cancer in post-menopausal women with disease progression following anti-estrogen therapy. Fulvestrant has limited water solubility and requires monthly intramuscular (IM) injections. Fulvestrant's aqueous insolubility creates a challenge to achieve and maintain efficacious serum concentrations.
Another class of anti-estrogens are selective estrogen receptor modulators (SERMs) which act as antagonists or agonists in a gene-specific and tissue-specific fashion. A goal of SERM therapy is to identify drugs with mixed profiles that afford beneficial target anti-estrogenic activity and either avoid adverse off-target effects or exhibit incidental beneficial estrogenic side effects. An example of a SERM is tamoxifen, initially sold by AstraZeneca under the name Nolvadex. Tamoxifen was also disclosed by ICI in U.S. Pat. No. 4,659,516, (see also U.S. Pat. Nos. 6,774,122 and 7,456,160). Tamoxifen is a prodrug that is metabolized to 4-hydroxytamoxifen and N-desmethyl-4-hydroxytamoxifen which have high binding affinity to the estrogen receptor. Tamoxifen is indicated to prevent further breast cancer after breast cancer treatment and to treat node-positive breast cancer in women following mastectomy and radiation. Tamoxifen can affect bone health. In pre-menopausal women, tamoxifen can cause bone thinning, while it can be beneficial for bone health in post-menopausal woman. Serious side effects have been noted, including increased risk of uterine cancer in post-menopausal women and “tumor flares” in women with breast cancer that has spread to the bone. In addition to these side effects, some women who initially respond to tamoxifen experience acquired resistance over time, and in some cases ER positive breast cancer not only becomes resistant to tamoxifen, but tamoxifen becomes an agonist which induces tumor proliferation.
A third line of treatment for breast cancer includes steroidal and non-steroidal aromatase inhibitors that block the production of estrogen and therefore block ER-dependent growth. These drugs, which include letrozole, anastrozole, and exemestane, have the risk of removing all estrogens from women after menopause, increasing the risk of bone thinning, osteoporosis, and fractures.
A number of SERDs, SERMs, and aromatase inhibitors have been disclosed. The SERM raloxifene was disclosed by Eli Lilly in 1981 (U.S. Pat. Nos. 4,418,068; 5,478,847; 5,393,763; and 5,457,117) for prevention of breast cancer and treatment of osteoporosis. In June 2011, Aragon Pharmaceuticals disclosed benzopyran derivatives and acolbifene analogs for treatment of tamoxifen-resistant breast cancer (see WO2011/156518, U.S. Pat. Nos. 8,455,534 and 8,299,112). Aragon became Seragon in 2013, and was purchased by Genentech in 2014. See also U.S. Pat. Nos. 9,078,871; 8,853,423; 8,703,810; US 2015/0005286; and WO 2014/205138. Genentech is now developing Brilanstrant (GDC-0810, formerly ARN-810) for the treatment of locally advanced or metastatic estrogenic receptor positive breast cancer.
Genentech disclosed a series of tetrahydro-pyrido[3,4-b]indol-1-yl compounds with estrogen receptor modulation activity in US2016/0175289 and a combination therapy of three compounds, one of which was GDN-0810, for estrogen receptor modulation in US2015/0258080.
AstraZeneca is currently developing AZD9496, a novel, oral selective estrogen receptor downregulator in patients with estrogen receptor positive breast cancer (WO 2014/191726).
Additional anti-estrogenic compounds are disclosed in WO 2012/084711; WO 2002/013802; WO 2002/004418; WO 2002/003992; WO 2002/003991; WO 2002/003990; WO 2002/003989; WO 2002/003988; WO 2002/003986; WO 2002/003977; WO 2002/003976; WO 2002/003975; WO 2006/078834; U.S. Pat. No. 6,821,989; US 2002/0128276; U.S. Pat. No. 6,777,424; US 2002/0016340; U.S. Pat. Nos. 6,326,392; 6,756,401; US 2002/0013327; U.S. Pat. Nos. 6,512,002; 6,632,834; US 2001/0056099; U.S. Pat. Nos. 6,583,170; 6,479,535; WO 1999/024027; U.S. Pat. No. 6,005,102; EP 0802184; U.S. Pat. Nos. 5,998,402; 5,780,497 and 5,880,137.
J-Pharma is currently developing benzothiophene compounds for the treatment of disorders related to urate transportation. See for example WO 2012/048058.
Bionomics LTD is developing benzofurans, benzothiophenes, benzoselenophenes, and indoles for treatment of tubulin polymerization related disorders. See for example WO 2007/087684.
Additional benzothiophene compounds are disclosed in WO 2010/127452, WO 2010/093578, WO 2009/013195, EP1947085, JP 2005-129430, US 2007/0112009, WO 2005/016929, EP0752421, EP0622673, EP0551849, EP0545478, U.S. Pat. No. 5,491,123, and WO 2006/084338.
Given the often devastating effects of estrogen-modulated disorders, including cancer, tumors, and in particular breast cancer, there remains a strong need to create new drugs that have significant anti-estrogenic efficacy without unacceptable side effects.